Diploid-triploid mosaicism (DSM) is a genetic condition caused by an abnormal number of chromosomes. Symptoms of this condition may include decreased muscle tone (hypotonia), slow growth, characteristic facial features, fusion or webbing between the fingers and/or toes (syndactyly), and unusual skin pigmentation. Intellectual disabilities may be present. DSM occurs when a person has some cells with three copies of each chromosome for a total of 69 chromosomes (triploid cells) and some cells with the usual 2 copies of each chromosome for a total of 46 chromosomes (diploid cells). Having two or more different cell types is called mosaicism. Diagnosis of this condition is made based on a clinical exam and a skin biopsy. Treatment is based on managing the symptoms.

The following list includes the most common signs and symptoms in people with diploid-triploid mosaicism. These features may be different from person to person. Some people may have more symptoms than others and symptoms can range from mild to severe. This list does not include every symptom or feature that has been described in this condition.

Signs and symptoms may include:

• Growth delay
• Decreased muscle tone (hypotonia)
• Characteristic facial features
• Uneven facial and/or body growth
• Fusion of the fingers or toes (syndactyly)
• Intellectual disability
• Developmental delay

Signs and symptoms of diploid-triploid mosaicism are present at birth. Developmental and intellectual disability may also be present. Some people have feeding problems, unusual skin pigment, and fat around the stomach. Very few people have been reported with this condition and so little is known about how this condition changes throughout someone's life.

Diagnosis of diploid-triploid mosaicism is based on a clinical exam, the symptoms, and testing to examine the chromosomes from different types of cells. Testing generally includes a skin biopsy or the investigation of urinary cells.

• Medical geneticist
• Neurologist
• Gastroenterologist
• Developmental specialist